Plusbus is not true fare integration, it's an afterthought bolted on to the rail ticketing system that only works in random areas of the country, is inexplicably unavailable from some stations even within those areas, is absolutely useless if your journey starts on a bus rather than a train, and is nearly useless anyway because it's quite likely the driver won't recognise it.
I'm doubt this is really what's suppressing rail passenger numbers though.
I'm becoming convinced that "We need a rolling electrification scheme" is some sort of fundemental particle of RailUK threads - in that any thread on this website, left long enough, will eventually be reduced to that statement.
Of course it's very true that it would be a good idea, but would it really increase passenger numbers that much? I can't imagine so, especially not in the short term.